Balboa Island Seawalls Rehabilitation Project

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The Tidelands Management Committee pro-actively began discussions for protecting Balboa Island in 2011. Discussions have become more detailed as options are considered for protecting public safety and property in a cost effective manner.

 

The committee is discussing uncertainties associated with future sea level rise, accessibility to docks and the beach, and the need to preserve the wonderful experience of walking the Islands’ boardwalks. At the next meeting in early 2015, City staff will make a presentation to the Tidelands Management Committee that will focus on seawall rehabilitation options and costs.

 

For a complete schedule of Tidelands Management Committee Meetings, please click here.

 

July 14, 2015 Study Session Seawall Presentation

 

October 29, 2014 Seawall Presentation

 September 17, 2014 Seawall Presentation

 

More information on the following is coming soon:

  • Measured sea level rise along the West Coast
  • Existing elevations around the harbor
  • FEMA flood insurance requirements

The City of Newport Beach is planning for the rehabilitation of the aging seawalls around Balboa Island and Little Balboa Island (Islands) to maintain the structural integrity of the seawall system and protect the Islands from flooding due to storm surges and high tide conditions.

1. How old are the seawalls around Balboa Island and Little Balboa Island (Islands)? What is their projected useful life?
The seawalls were first built in the 1920’s and 30’s and are between 75 - 85 years old. In recent years, a cap extension (Figure 1) was added to the bulkhead beam on some portions of the seawall to provide added flood protection.

Figure 1: Seawall Cap Extension

Little Balboa Seawall Cap Extension

 

These seawalls have performed well in protecting the islands from flooding, but are now showing their age. The (exposed) walls are estimated to have between 10-25 years of remaining useful life. The walls along the north side of Balboa Island are largely covered in sand and the condition of these walls has not been examined. It is possible this reach of the seawall and other similar protected reaches around the islands may, with routine maintenance, have a longer remaining service life.

More information on the condition of the seawalls is available in the City’s assessment report from April 2011:

2011 Assessment Report

 

2. Are the seawalls around the Islands high enough to provide adequate flood protection?
Presently yes, however, there are a few segments around Balboa Island that are not quite high enough should we experience extremely high tides and waves. The photo in Figure 2 shows the water overtopping the existing seawall in December 2010 when the Islands were hit with a moderate storm surge at high tide.  Figure 3 shows the sea level near the top of the Balboa Island seawall on December 12, 2013 during a king tide with no wind or waves.

Should there be further rise in sea level; longer segments of the existing seawall around Balboa Island could be subjected to this overtopping. The Little Balboa Island seawall is somewhat higher than the Big Island due to a project in the 1980s that raised the cap. South facing sides of both islands can be more susceptible to periodic overtopping from wave run-up through the harbor jetty with large storm surges or wind driven waves.

Figure 2: Moderate storm surge during a high tide in December 2010 

Figure 2 Storm 2010

 

Figure 3: King tide on a calm day at the West Side of Balboa Island – December 12, 2013

Figure 3

 

3. What are the existing top-of-seawall elevations?
Table 1 summarizes the range of existing top-of-wall elevations for each side of the Islands. Figure 4 shows more detailed information of the existing top of seawall elevation around the Balboa Islands. Note that two elevations are given at each measure point. The top elevation is based on the NAVD88 datum (a fixed vertical datum) and the bottom elevation is based on the Mean Lower Low Water datum (a variable, ocean-based, vertical datum). The NAVD88 datum is preferred as it is a fixed datum not subject to changes in sea level.

Table 1: Existing Top of Wall Elevations (NAVD88)

Balboa Island

Little Balboa Island

North Side

7.7-8.3’

 North Side (same as  East side)

8.6-9.1’

East Side (Grand Canal)

8.5-8.7’

West Side (Grand Canal)

8.5-8.6’

South Side

7.8-8.3’

South Side

8.6-9.3’

West Side

7.8-8.2’

East Side

8.6-9.1’


Figure 4: Existing Top of Wall Elevations on the Balboa Islands.

Figure 4

4. How high are sea levels expected to rise?
There is a lot of work being done to predict future sea level rise over the next few hundred years. Table 2 lists recent studies. All these studies predict a significant rise in sea level over the next 85 years.

In 2009, the California State Coastal Conservancy adopted a Climate Change Policy that agencies should plan for a 55-inch sea level rise by 2100. This projected 55-inch sea level rise by Year 2100 was used as the basis for the analysis in the City’s 2011 study entitled Assessment of Seawall Structural Integrity and Potential for Seawall Over-Topping.

Table 2: Recent sea level rise reports with predictions for sea level elevations in Year 2100. Note that the ”95%” column on the right hand side of the table level indicates there is a 5% chance the predicted increase in sea level will be exceeded. 

Agency

Year

95%

50%

5%

IPCC 4th Assessment

2007

9”

15”

20”

Vermeer and Rahmstorf

2009

39”

49”

61”

US Corps of Engineers

2011

17”

39”

59”

National Academy of Sciences

2012

17”

37”

66”

IPCC  5th Assessment

2013

17”

24”

31”

Quaternary Science Reviews

2014

28”

37”

47

 

5. Why are there such large differences in the predictions?
There are two dynamical methods presently used to project sea-level changes during the next century: 1) physical, process-based models and 2) semi-empirical models. Semi-empirical model projections significantly exceed process-based projections.

Physical process-based models aim to describe quantitatively the different physical processes that contribute to sea level rise. The process-based method relies on coupled atmosphere-ocean models to estimate the effects of thermal expansion and on sea-level models combined with certain empirical relationships to determine the influence of land-ice mass changes. The most conservative sea level rise is predicted by Intergovernmental Panel on Climate Change (IPCC). The IPCC uses the process-based methodology. Between 2007 and 2013, the IPCC has increased its sea level rise prediction (95% confidence) from 20 inches to 31 inches.

Semi-empirical models try to exploit the link between observed sea level rise and observed global temperature changes in the past in order to predict the future. The semi-empirical method uses various physically motivated relationships between temperature and sea level, with parameters determined from the data, to project total sea level. National Academy of Sciences and Vermeer and Rahmstorf use semi-empirical models.

6. Would raising the seawalls reduce or eliminate flood insurance requirements?
Perhaps, but more study and FEMA review is needed. Please visit their website at www.fema.gov/national-flood-insurance-program.

7. Where would the new seawall be built relative to the existing seawall and what material would the seawall be?
The new seawall is recommended to be built on the waterside of the existing seawall (Figure 5). The new seawall will be made up of steel H-piles with concrete planks. Cathodic protection will be required for the steel H-piles to keep them from corroding. The existing pile cap will be removed and the boardwalk will be widened approximately 1.5 feet. The boardwalk may remain at the existing elevation. The design will explore opportunities to raise the boardwalk in conjunction with raising the seawall along certain reaches of the seawall. These opportunities would be discussed with the adjacent property owners.

Figure 5: Proposed new seawall built on the waterside of the existing seawall.

Figure 5

8. What would the top of wall elevation be for the new seawall?
The City is considering three basic options for constructing new seawalls and/or raising the existing seawall cap:

Option 1 - New seawalls at Elevation 10.0 feet (Figure 6)
a. Construct new seawalls to Elevation 10 feet (NAVD88) around most of the Islands (Figure 6 pink and blue sections) and raise the cap on the north side of Balboa Island (yellow section) to Elevation 10 feet. 
b. If sea levels continue to rise, in about 50 years, replace capped seawall on the north side of
Balboa Islands (yellow section) with a new seawall constructed to minimum Elevation 10 feet.


Option 2 - New walls at Elevation 9.5 feet (Figure 6)
a. Construct new seawalls to Elevation 9.5 feet (NAVD88) around most of the Islands (Figure 6 pink and blue sections) and raise the cap on the north side of Balboa Island (yellow section) to Elevation 9.5 feet.
b. If sea levels continue to rise, in about 40 years, add a minimum of 6-inches to the new seawalls (pink and blue sections) and replace the capped seawall on the north side of Balboa Islands (yellow section) with a new seawall constructed to minimum Elevation 10 feet.

Option 3 – Cap extensions with limited new wall construction (Figure 7)
a. Construct new seawalls on the west of Balboa Island (black section) to Elevation 9.5 feet.
b. Construct new seawalls on the Grand Canal to Elevation 9.5 feet south of the Park Avenue Bridge and Elevation 9.0 feet north of the bridge.
c. Raise the pile cap to 9.5 feet on the south side of the Islands.
d. Raise the pile cap to 9.0 feet on the north side of the Islands.
e. Raise the pile cap on the east side on Little Balboa Island (9.0-9.5 feet as shown in Figure 7).
f. If sea levels continue to rise, in about 30 years, raise new seawalls to minimum Elevation 10 feet and replace all capped seawalls with new seawalls to minimum Elevation 10 feet.

Figure 6: New seawall and cap extensions for Options 1 or 2. (Please click on the photo to enlarge)

Figure 6

Figure 7: New seawall and cap extensions for Option 3. (Please click on the photo to enlarge)

Figure 7

9. What are typical top of seawall elevation at other harbors?
The top elevation of seawalls at other southern California harbors is 9.5 feet (NAVD88) or higher. (See Table 3.)

Table 3: Harbor Top Elevation (NAVD88)

Agency (Harbor)

Top of Wall Elevation (NAVD88)

County of Orange (Dana Point)   

9.62’

County of LA (Marina del Rey)       

9.62’ - 11.62’

City of Huntington Beach (General)

9.62’

City of Long Beach (Alamitos Bay)  

9.62’

City of Long Beach (Naples Island)

9.50’ (planned)

10. Which option is best?
Table 4 compares the estimated schedule and costs for constructing new seawalls and/or raising seawall caps for the three options described above. The cost estimate include costs for providing access for private and public piers, providing beach access over the higher seawalls, providing flood protection at the ferry landing and at the Collins Island Bridge, and providing ADA access of the boardwalk adjacent to the Mariner’s Bridge. All costs are in today’s dollars and include a 25% contingency. Option 1 provides the best flood protection and the lowest overall, long-term cost. Option 3 has the lowest initial cost and would have the least impact on view planes.

Table 4: Projected duration of flood protection and estimated cost for seawalls and associated improvements for the three options. 

 

Option 1

Option 2

Option3

Year ~2020: Initial construction cost (w/ 25% contingency)

$69 million

$69 million

$34 million

Projected flood protection until:

2063

2056

2047

If sea levels will rise above Elevation 9.0 feet, under Option 3, before 2047 the new seawalls would need to be raised and capped seawall sections would need to be replaced by new seawalls at an approximate cost of $57 million.

If sea levels will rise above Elevation 9.5 feet, under Option 2, before 2056, the new seawalls would need to be raised and aging capped seawall sections would need to be replaced by new seawalls at an approximate cost of $19 million.

Under Option 1, before 2063, aging capped seawall sections would need to be replaced by new seawalls at an approximate cost of $16 million.

11. When would the seawalls be constructed? How long would the construction take?
Before construction can begin, the City will need to design the seawalls and other related improvements and obtain a Coastal Development Permit from the California Coastal Commission along with several other permits from State and Federal agencies. That process could take 3 or more years. The seawall construction would likely be performed in two phases over a 5-year period with the seawalls of most concern, the Grand Canal and West End of Balboa Island, being in the first phase. The second phase would likely be the south sides of the Islands as they are more susceptible to waves from storms. The third phase may be the east side of Little Balboa Island with the final phase the north side of Balboa Island. The north side of Balboa Island is the most protected side from storm surges; however, these walls will also need to be reconstructed and raised in the event of sea level rise. Other items that would be constructed include access ramps for the public and private piers, beach access ramps, flood protection measures at the Ferry Landing, access modifications to Collins Island and boardwalk access modifications near Mariner’s Bridge.

12. Will we be raising the adjacent Boardwalk?
The City plans to maintain the existing boardwalk elevation for now unless there is an opportunity to raise along certain reaches. Staff would discuss options with the property owners adjacent to the reach of interest.

13. How will private dock access be addressed?
The various interface between private docks and the seawall; i.e. steps, platforms, etc., have been addressed as part of the seawall project in order to provide safe access. Proposed design options and style concepts are under development and will be posted in March 2016.

14. How will the beach be accessed?
The proposed design is under development.

15. If the boardwalk is raised, what about drainage from my property?
The project design will include proper drainage for both public and private property.

16. Who owns the seawalls around both islands?
The City of Newport Beach. In addition to the seawalls, the City is responsible for the streets and sidewalks; streetlights; and sewer, water and storm drain facilities.

17. Who will pay for the seawall project?
The exact method of payment is still under review as the concept and details are being developed.

18. Who can I contact if I have additional questions?
Please send your comments and questions to seawalls@newportbeachca.gov. Assistant City Engineer Bob Stein will be reviewing and responding to your emails.